This invention relates to an electrical circuit, and in particular, to an electrical circuit that limits the current through a light emitting diode.
Incandescent lamps are used in a wide array of environments and have generally found substantial commercial success in meeting various demands. More recently, industry is seeking an alternative light source that has an extended life and can endure the rigors of applications that experience mechanical vibration or shock, a problem area for relatively fragile filaments or coils of an incandescent lamp. An exemplary use of an incandescent lamp in this type of environment is in household appliances such as vacuum cleaners. Incandescent lamps have been widely used in vacuum cleaners in the past. However, the incandescent lamp encounters a great deal of mechanical shock when the vacuum cleaner is in use and is thus subject to mechanical failure. As a result, incandescent lamps have a shorter life and require frequent replacement.
Light emitting diodes (LEDs) have been suggested as alternative light sources for incandescent lamps due to their robust structure that is able to withstand mechanical vibrations and the long life associated with their efficient operation. In this environment, a source current is much greater than the maximum current allowed for LEDs. To limit the current through the LEDs, it is known in the art to use resistors once alternating current (AC) has been converted to direct current (DC) such as by bridge rectifiers. One problem associated with this approach is the thermal issue associated with such circuits because resistors heat as they dissipate electrical energy. Further, proper heat dissipation is necessary because improper heat dissipation is a leading cause of resistor failure. Thus, many of the energy benefits offered by the alternative use of LEDs as the light source are eliminated.
Another problem with this approach is that there is only a very limited electrical area or compartment typically associated with household appliances. Thus, the diodes and the current limiting components must be configured to fit within this compact area without overheating the area and causing component failure.
Another suggested approach to limiting the current supplied to LEDs is eliminating the rectifier and connecting the resistor in series with a pair of oppositely polarized LEDs. The inefficiencies of the rectifier circuit, however, are not solved since a resistor is still employed as the current limiting device.
Yet another approach to limiting current is employing an inductor connected with a pair of oppositely polarized LEDs. Due to the size of inductor required, this method is not desirable for use where space is constrained. Additionally, ideal inductors cannot support a DC voltage and thus, cannot correct for imbalances in the diodes.
Accordingly, a need exists for an alternative manner of limiting current.
The present invention provides a more cost efficient electrical circuit for limiting current.
The present invention uses only a few components and takes up less space in an electrical compartment.
Current is limited by the reactance of a capacitor rather than by resistance or inductive reactance. A current limiting circuit for a diode comprises a capacitor coupled to a load and at least two diodes, the diodes being oppositely polarized and connected in parallel.
In another embodiment, the capacitor is coupled to at least one pair of oppositely polarized diodes connected in parallel.
In yet another embodiment, the capacitor is coupled to two oppositely polarized parallel branches of diodes.
This circuit has a number of advantages over the prior art. The current limiting circuit only requires three components, namely one capacitor and two LEDs connected to a load, namely an AC source. This circuit occupies less space in an electrical compartment than any of the prior art circuits.
Another advantage resides in the use of a capacitor which is more cost effective and compensates for any DC voltage imbalance.
Still another advantage is realized since capacitors are more efficient than resistors and inductors.